1. Field of the Invention
The present invention relates to compound bows for use in archery. More particularly, the present invention relates to a fast shooting, highly accurate and easily strung compound bow which may utilize only a single spring for providing a propelling force to an arrow.
2. Related Art
Historically, bows have been developed and modified to increase arrow velocity and accuracy, yet concurrently decrease the force required to hold the bow in the fully drawn position. As an improvement to the traditional single-piece recurve bow, multiple-piece compound archery bows were developed. In one type of compound bow, cam pulleys are pivotally mounted to the outer ends of the bow arms. Such cam pulleys serve to increase the energy stored in the bow when drawn, without increasing the length of the draw or the holding force required in the fully drawn position. In another type of compound bow, a rigid central handle section is provided and bow arms are pivotally coupled to opposite ends of the handle section. Use of various mechanisms to rapidly pivot these arms upon release of the bow string allows greater force to be imparted to the arrow compared with traditional bows, without adding the mass of cam pulleys to the rapidly moving distal ends of the arms. However, such compound bow designs frequently apply different amounts of torque to the upper and lower cam pulleys or bow arms and produce uncoordinated rotation or pivoting of these cam pulleys or bow arms. As a result, the bow string may not apply a propelling force to the arrow directly along a line defined by the axis of the arrow shaft. This causes irregular and inaccurate arrow flight paths.
In an attempt to counter this problem, bow designers have added synchronization cables and pulleys to such bows to ensure synchronized angular rotation of the cam pulleys and bow arms. However, one problem with the typical compound bow involves the confusing complexity and possible safety hazards produced by the extra cables necessary to synchronize angular rotation of the cam pulleys and bow arms upon release of the bow string. Many presently available compound bows are designed such that the synchronizing cable/pulley mechanisms are located between the central handle section of the bow and the archer. These designs are inherently hazardous in that if the bow string or a cable breaks, dangerous snapping and pulling of the loose string and cables could occur directly in the face of the archer. Also, the additional mass of these synchronizing pulleys and cables slows rotation of the cam pulleys or bow arms, thus decreasing arrow velocity.
Another problem with such designs is that the hand grip is conventionally centered on the bow such that the archer holds the bow midway between its top and bottom. This means that the arrow will be nocked above the center of the bow and thus closer to the upper cam pulley or bow arm than to the lower cam pulley or bow arm. As a result, even if the synchronizing cables and pulleys are successful in achieving exactly synchronized rotation of the upper and lower cam pulleys or bow arms, and in applying exactly equal torque to both cam pulleys or bow arms, the bow string will still not apply a propelling force directly along the arrow shaft. Thus, such designs are inherently flawed.
In another attempt to overcome problems inherent in previously known bow designs, a single spring device has been mounted to the central handle section of a bow. One bow arm, the "master" arm, is attached directly to the spring device by rigid mechanical linkages Another bow arm, the "slave" arm, may be attached to the master arm with a cable routed through the central handle section of the bow. Unfortunately, however, with this design, substantial synchronization errors may be produced by the stretching of the cable interconnecting the master and slave arms. That is, the master arm will begin to rotate immediately upon release of the bow string because this arm is connected by rigid mechanical linkage to the spring. There will then be a time delay, as the interconnecting cable stretches, before the slave arm will also begin to rotate. Thus, accurate coordination of the bow arms when the bow string is released would appear to be difficult or impossible using this design.
In a variation of this design, instead of a cable, rigid mechanical linkage interconnects the master and slave arms. However, like the cable, the interconnecting linkage may also be subject to stretching, and will therefore have the same adverse effects associated with the previously mentioned design. Moreover, if the linkage or interconnecting cable is made sufficiently heavy such that no appreciable stretching occurs, then the added mass will slow rotation of the arms upon release of the bow string. Furthermore, the "play" in the hinges interconnecting the bow arms with the linkage adds to the problem of properly coordinating bow arm rotation.
Also, when a conventional compound bow is in the released or "braced" position, the bow arms extend in almost exactly opposite directions. Thus, any rotational force on the arms can be resisted only by a much larger tension in the bow string. As a result, many conventional bow designs require that, to avoid breaking the bow string, the bow arms sustain only a relatively small rotational force when in the braced position. The energy stored in the bow in the braced position is known as the "pre-load". As a result of this limitation on pre-load, the initial portion of the draw in conventional compound bows is substantially wasted since only a small amount of energy is added to the bow when the archer first begins to draw back the bow string.
Greater accuracy and arrow velocity may be achieved if the rotation of the bow arms could be properly coordinated, without the use of a complicated synchronizing pulley and cable system, and if greater amounts of energy could be stored in the bow during the initial portion of the draw.